The Carver Amp Challenge and the 21st Century and it's Failure

great post, keep em' coming.
Larry

@spatialking Apologies, I seem to have been very much in error. You were right. I was wrong.

Best,
E

Thanks for the clarifications, @almarg I was not aware of the earlier testing with the ML, so my thinking about the current improvements was probably not accurate.

I appreciate your detailed and informative corrections!

What this keeps tickling me of is the Technics digitally controlled Class D amplifier. They use DSP to pre-correct issues the amplifier has with the load. Amplitude and phase issues Class D amps tend to have in the top octaves.

I wonder if today we couldn't make better models, or get a better idea of what amps are doing, in such a way that would allow us to pick a sound.

Best,

E

Good thread, Erik, and good points in your OP!

To clarify some historical facts about the "Carver Challenge":

Aczel’s preprint of the amp matching effort Carver performed under his auspices was written sometime prior to January, 1983, while the Stereophile article appeared in October, 1985. So Carver’s effort with Aczel was performed well before the one with Stereophile, although the people at Stereophile were apparently unaware of it when their article was written.

Also, "The Audio Critic" didn’t quite go defunct; it resumed publication in late 1987, after a lapse of about six years during which time Aczel served as president of the Fourier Loudspeaker company (which did go defunct during that time, for a variety of reasons Aczel later described in TAC as including inadequate capitalization, too few dealerships, and a warehouse fire).

The target amp that was the subject of the Stereophile article, as stated in footnote 3 on the first page of the article Erik linked to, was a Conrad-Johnson Premier Four tube amp. The target amp that was the subject of Aczel’s article was a Mark Levinson ML-2, a very highly regarded and very expensive solid state pure Class A monoblock amplifier of the time, rated at about 25 watts into 8 ohms but capable of providing huge amounts of current and much greater power into low impedances.

The null test, as described by Aczel, was performed by connecting Carver’s amp and the target amp in the normal manner to speakers that were at inaudible locations, and connecting a monitor speaker and/or a meter at an audible location between the + terminals of the two amps, both amps being provided with identical inputs.

Although Carver was able to tweak his amps to obtain a remarkable null of 70 db or so in those efforts, as I recall he pretty much admitted in an interview with "The Absolute Sound" about 7 or 8 years ago that he couldn’t come close to maintaining that deep a null in production. And as Erik pointed out, the null was achieved with one specific speaker load.

I owned both the original M400, the cube-shaped amplifier in which Carver introduced his magnetic field power supply technology but which was not "transfer function modified" to emulate a different amp, and the subsequent M400t version which was designed to emulate the ML-2.

IME the original M400 sounded very poor, with a strange glare often being present. The M400t sounded surprisingly good, and was certainly an excellent value in relation to its price and its 200 wpc power capability. The most significant weakness in my experience with the M400t, using it with fairly easy-to-drive 7 ohm 90 db speakers, was that the size of the image it projected seemed somewhat constricted. But based on my experience with the two amps it would certainly seem that Carver’s efforts to emulate the sonics of the ML-2, and the technique he used in that process, provided considerable benefit.

Regards,
-- Al

PS, you may be a little confused since I think Carver may have used the term "current source" to describe the difference. That  doesn't mean more current. It's a different operating principle than a voltage source.

It started with a bold claim from Carver stating his amplifier was indistinguishable from a tube unit.

His first claim was he could make it indistinguishable. Not that it started there. After that he produced amps such as the M500t. He may have produced others on this same idea, and it's arguable how well he succeeded.

His amp may ONLY have been an accurate reproduction of the CJ amp with 1 particular speaker. In any event, I don't claim his success, but I do claim his revolutionary way to evaluate equipment has not carried us forward, and that's disappointing.

one of which was increasing its current capacity significantly 

Not my understanding. Among other things, Carver increased output impedance, going the opposite way.

don't agree that most of our measurements are stuck in 1970 technology. The test equipment we have today is like comparing a Lotus to a Model T

Which has not actually revolutionized our understanding. We, the buying public, read reviews and measurements taken with test gear which can add more zeroes to the distortion measurements and more dB to the S/N measurements compared to that in the 1970s but we are not presented with revolutionary ways of understanding the performance of electronics and their audibility. 

Likewise, I don't agree that no one has made improvements in measurements.   Folks have, I just don't see them dumping their IP into public domain for their competitors to use.

It's quite plausible this is true, and that leaves us, again the buyers, in exactly the same place as if it didn't exist. We as consumers are stuck with 1970s definitions of electronics measurements, despite vastly superior measurement possibilities, disk storage space, CPU power to now investigate the dynamic performance of gear in entirely new ways.


Best,

E

Yeah, that was part of the story.   It started with a bold claim from Carver stating his amplifier was indistinguishable from a tube unit.  I believe Peter Aczel picked up the story in his review magazine, The Audio Critic.   When it wasn't the same, Carver had to modify his amplifier in significant ways to make it sound the same, one of which was increasing its current capacity significantly.   Those mods never made it into production since they were much too expensive.  

Tweaking time domain energy here and there, that has all been done before, although I think Bob was the first to apply it to audio work, ignoring tone controls and equalizers, of course.   Aczel's magazine went defunct before the review was published but Bob still reprinted that review with permission to sell his amplifiers.

I don't agree that most of our measurements are stuck in 1970 technology.  The test equipment we have today is like comparing a Lotus to a Model T. I wish I had today's stuff back in my audio design days!  Back then, we used to laugh and say "the test equipment we have today is like comparing a Lotus to a Model T" when we talked about 1970 technology compared to the 1950 technology.  However, I find myself saying the same thing today about current test equipment.   I can do things in my lab today with 1995-2005 era used equipment that I could never do in the 70's.  And, the best part, it is so much less expensive today than back in the 1970's when comparing performance to the dollar.

Likewise, I don't agree that no one has made improvements in measurements.   Folks have, I just don't see them dumping their IP into public domain for their competitors to use.    See, the thing is, audiophiles want a single measurement that is the cornucopia and tells all.   That is unlikely to happen, the fact is our equipment is fine, the key is knowing how to apply the equipment, how to interpret what you are measuring, and then solving the problem.